The present disclosure relates to a content addressable memory and is particularly applicable to the content addressable memory which is able to be built in a semiconductor device and the semiconductor device in which the content addressable memory is built.
A storage device which is called an associative memory or a CAM (Content Addressable Memory) is adapted to search for a data word which matches a search word (search data) from among data words (entries) that the storage device stores therein and to output an address of the data word in a case where the data word which matches the search word is found.
There are a BCAM (Binary CAM) and a TCAM (Ternary CAM) in the CAM. Each memory cell of the BCAM stores information of either “0” or “1”. On the other hand, each memory cell of the TCAM is able to store information of “don't care” in addition to the information of “0” and “1”. “don't care” indicates that either “0” or “1” will do.
A TCAM device using a TCAM is widely used for address search and access control in a router for a network such as the Internet. It is expected that everything is coupled to a network such as IoT (Internet of Things). In IoT, demand for a TCAM is increasing like routing of a network. In a general TCM, however, the speed and the scale of a system increase, so it has come to be demanded to provide a TCAM device in a semiconductor chip as a system on a chip SoC.
Patent literature 1 (Japanese Unexamined Patent Application Publication No. 2017-45495) discloses an example of a TCAM device using a TCAM.